Math question retail sales?

According to my memory of retail accounting 50% Mark means that one half (50%) of the price is mark up. I.e. if an item costs a retailer $50 apply 50% markup rule would set the price as $100

No. A 50% margin means half the price is markup. (And the markup would be 100%). A 50% markup on an item costing $50 would yield a price of $75. Are you using the word “mark” to refer to “margin”? If so, we are saying the same thing. If you are using the word “mark” as a short of “markup”, then you are incorrect.
 
I have owned a retail electronics store and I can tell you that the over all margins was about 30 percent. On big ticket items much less and on accessories much higher
 
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The question is anyone in retail.
This is not a question.
The short response to what you are trying to ask is that, as a very general rule (with many exceptions), many products are marketed at a retail price which is twice the wholesale cost.
In other words, the wholesale price is 50% of the retail price (that's the 50% you are referring to), so the retail added "mark up" is actually 100% of the wholesale cost.
 
Anyone in retail want to detail what their mark ups are in general? I've read it's generally double as a rule of thumb.

In apparel it is often 100% or a bit more. A retail chain that turns in a consistent 52% - 55% gross margin can bottom line around 10% if they are well-run.

And yes, I have deep expertise in this area.

Why do you ask?

KK